1. Field of the Invention
The present invention generally relates to eye tracking systems for a variety of systems, including human computer interfaces, and more particularly to an inexpensive interferometric eye tracking system.
2. Background Description
Human-computer interactions pose some of the most difficult challenges in the design of personal computer systems. The runaway success of the TrackPoint II.TM. pointing stick in differentiating and promoting IBM's ThinkPad.TM. notebook computers is well known. The success of that device was due to its novel design. Specifically, the pointing device is placed right in the home row of the keyboard so that the user needs not take his or her eyes off the screen to use the pointer. Although not as precise as a mouse or trackball for graphics applications such as drawing, the pointing stick offers effortless usability in text-based applications such as word processing, spread sheets, and databases (which is where most users spend most of their time), and in coarse-resolution graphical tasks, such as navigating the graphic user interface (GUI) shell. Particularly for mobile use, this is a very favorable tradeoff.
The success of GUIs and pointing devices in making computers easier to use has been universally acclaimed, almost to the point of obscuring the residual annoyances and inefficiencies in such an interface. For example, although GUI windows have a carefully defined Z-order (i.e., which one is logically on top of which), it is not currently possible to look around the upper window to see what is below it, not to lean forward to take a closer look (and have the magnification change automatically). Both of these actions are very important in making an on-screen "object" more like a physical object. At least as annoying as these is the shift of attention involved in moving the mouse cursor around the screen to the point the user is looking at. This operation distracts the user from his or her task, and so impeded his or her work, especially since it is repeated dozens or even hundreds of times a day. It would be tremendously valuable to have an accurate, robust eye tracking system which could quickly put the mouse cursor within a few pixels of the gaze point.
Eye tracking systems have been in low-level use for more than twenty years, but have never caught on, despite considerable amounts of work by the military and others. This discouraging history has been largely due to the non-ideal characteristics of existing eye tracking systems. Current generation eye trackers work by sensing the position of the glint from the cornea, due to a small area light source, and fall in two major groups; one using head gear, and the other, video equipment.
Eye trackers based on head gear generally use a light source, such as a light emitting diode (LED), and a position-sensing detector such as a lateral-effect photo diode to measure the direction of the corneal glint with respect to the head gear. Other methods, such as triangulation based on magnetic direction sensors, are needed to obtain the orientation and position of the head gear with respect to the computer screen, in order to determine the gaze point. Systems used in physiological research usually clamp the subject's head into a table-mounted fixture. Even in the computer game field, the market for such a system would probably be rather limited.
The other class of systems, those using cameras rather than headgear, typically use a charge coupled device (CCD) camera/frame grabber combination to acquire an image of the subject's head, with the corneal glint showing. This sort of system overcomes the inconvenience and discomfort of the headgear-based systems, but at a price in cost and accuracy. Extensive image processing is required to locate the subject's face and nose in the camera's field of view, following which further processing can recover the position of the corneal glint with respect to the nose, and hence the direction of gaze. This procedure is complex, since the motion of the corneal glint is very small (a few millimeters) and the motion of the subject's head is many times larger, so that the precision obtained with cameras of reasonable cost is quite low, in spite of the expensive equipment required. In addition, such systems have great difficulty with people having hooded eyes or wearing eye glasses.